The present invention relates generally to magnets for use with a neutron scattering apparatus and, particularly, to a high field repeating pulsed magnet having multiple layers of conductor with aluminum split at its mid-plane to allow neutron scattering through large angles.
Neutron scattering is a valuable tool for probing solids and liquids in many fields, including materials science, medical science, engineering, condensed matter physics, chemistry, biology, and geology. In general, neutron scattering involves probing a sample with thermal neutrons generated in a research reactor or accelerator. A neutron, which is an uncharged magnetic subatomic particle, has a wavelength about equal to the spacing between atoms in molecules. As such, neutrons can produce interference patterns from the atomic lattice of a sample. As an incident beam of neutrons passes through it, the atoms in the sample cause the neutrons to scatter. The scattering pattern reveals detailed information about the sample""s atomic structure and dynamics.
Those skilled in the art recognize the need for an apparatus that combines neutron scattering with the ability to analyze materials under high magnetic fields. A powerful magnet surrounding a sample that is targeted by the neutron beam permits investigation into aspects of the sample""s structure otherwise undetectable by conventional means. Although various magnets have been proposed, a pulsed magnet is desired for use with a pulsed neutron source to permit researchers to look at, for example, the three-dimensional arrangements of the magnetism in solids at microscopic levels.
As described above, a conventional neutron scattering apparatus sends bursts, pulses, or steady streams of neutrons through a sample. Three-dimensional xe2x80x9cmapsxe2x80x9d of the sample""s atomic structure appear as some of the neutrons are scattered by the magnetic elements in the sample. A magnet is desired for subjecting the sample to intense magnetic fields while neutron bombardment takes place. In doing so, the analysis provides additional information about the sample not available from neutron scattering alone. Traditionally, these intense magnetic fields are created by superconducting dc (steady-state) coils. Unfortunately, the upper critical field of today""s superconductors is around 25 tesla (T). Hence, superconducting magnets available for neutron scattering are presently limited to 15 T. There are many experiments for which higher fields are desirable. It may be possible to build a superconducting magnet with field strength close to 20 T but the space required for such a system would be inconveniently large. Alternatively, it may be possible to build dc resistive magnets with field intensities in the 30 T range. However, the cost to construct such a system might be prohibitive (e.g. around $40 million). To provide fields above 15 T at reasonable costs, Prof. Motokawa at Tohoku University teaches the use of repetitively pulsed magnets. Other high-field pulsed magnets are flushed with liquid nitrogen between pulses, generally requiring 30 minutes or more between pulses.
Presently available repetitively pulsed magnets face considerable problems in withstanding the stress and heat created by the electrical currents required to generate strong, rapidly firing magnetic pulses. In a single day""s operation, a high field repetitively pulsed magnet used in neutron scattering experiments may endure more structural strain cycles from pulses than most traditional high field magnets experience in their operational lifetimes. Conventional dc resistive and superconducting magnets, for example, are only able to operate reliably over about 10,000 repetitions due to the fatigue stress limitations. Higher fields and faster pulse rates are desired for improved resolution. Unfortunately, such improvements lead to even greater stresses on the magnet.
Researchers have proposed the use of a repeating pulsed magnet for providing substantially higher magnetic fields for use in neutron scattering. To date, such magnets fail to provide sufficient field strength and operational life span. In addition, they do not permit large angle or multi-angle scattering capability. Rather, such a magnet limits neutron scattering detection to a single angle relative to the incident beam, i.e., through a beam hole in the magnet.
For these reasons, a cost-effective magnet is desired for use with a neutron scattering apparatus for providing a high magnetic field to samples to study neutron/solid and x-ray/solid interactions and scattering and for permitting multi-angle scattering.
Among the several objects of this invention may be noted the provision of a magnet for use with a neutron scattering apparatus; the provision of a method for analyzing the atomic structure of a sample with a repeating pulsed magnetic field; and the provision of such magnet and method which are economically feasible and commercially practical.
Briefly described, a magnet for use with a neutron scattering apparatus embodying aspects of the invention includes a conductive coil that has a first body portion and a second body portion of high conductivity material, and a mid-plane portion in which the sample under analysis is positioned. The neutron scattering apparatus provides an incident beam of neutrons to the sample under analysis. The first and second body portions of the coil are electrically connected to each other via the mid-plane portion of the coil, and the mid-plane portion of the coil is a conductive material that is substantially non-interactive with neutrons.
In accordance with another aspect of the invention, a method is provided for analyzing the atomic structure of a sample with a repeating pulsed magnetic field. The method includes positioning the sample within a mid-plane portion of a conductive coil. The conductive coil having a first body portion and a second body portion of high conductivity material that are electrically connected to each other via the mid-plane portion. The method further includes directing a neutron beam through an opening in the mid-plane portion of the conductive coil and toward the sample positioned therein. The method further includes energizing the coil to produce magnetic pulses at a repetition frequency of at least approximately 2 Hz and a peak field of at least approximately 30 T when the magnet is operating.
Alternatively the invention may comprise various other methods and systems. Other objects and advantages will become apparent to those skilled in the art from the detailed description herein read in conjunction with the attached drawings.